Increasingly, television broadcast signals include logos that are displayed on television screens over the broadcast programs as station identification. Typically, logos stay on the screen for considerably long periods of time without change in their intensities, colors, patterns and locations, etc. Hence, they may be annoying, and can cause problems such as the well-known screen burn on High Definition TV (HDTV) sets. As such, techniques have been developed for detecting the logos within the broadcast video signals, and removing or processing the logos to avoid the above problems.
On the other hand, the logos may disappear in some cases such as when the video programs change. Without promptly detecting the disappearance of the logo, and therefore stopping processing, annoying visual artifacts may result. Therefore, it is important to sense when the detected logo has disappeared. To that end, the pixel intensity value change has been examined to detect the fading of images in video signals, such as in U.S. Pat. Nos. 6,542,544; 6,084,641 and 5,245,436.
In U.S. Pat. No. 5,245,436, the pixel means of a frame and its previous frames are calculated and then the relative mean change between the means is determined to detect the fading of an image. Although the mean change can be extensively applied to detecting the fading/disappearance of a logo, such a method is not robust when the video signal contains noise. As such, more comprehensive measurements must be undertaken. Similarly, U.S. Pat. Nos. 6,542,544 and 6,084,641 present different approaches to detecting fading of images in video signals. However, neither considers the impact of noise.
Indeed, almost all video signals in the real-world applications contain noise (some at considerably high levels). There is, therefore, a need for a method and system for tracking and detecting the disappearance of logos within noisy video signals.